Control device for a burner and adjusting method

ABSTRACT

The invention relates to a control system ( 15 ) for a burner and a setting-up procedure. The control system ( 15 ) controls the air ratio for combustion using the ionisation electrode ( 16 ). For calibration, a change is carried out in a first parameter, and the subsequent change in a second parameter is observed. Accurate expected values for the change observed come from stored characteristic data that have been determined in the setting-up procedure, and from taking into account the current combustive content of air and fuel. This allows corrective measures or fault signals to be established.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a control system.

2. Description of the Prior Art

The control system ensures that in a burner the ratio of the amount ofair to the amount of fuel, called the air ratio or lambda, is matched inthe whole performance range. As a rule lambda should be slightly abovethe stoichiometric value 1, for example, 1.3.

In a manner different to controlled burners, burners adjusted accordingto the air ratio react to external influences that change thecombustion. For example, the combustion can be re-adjusted after achange in the type of fuel or the air density. It has a higher degree ofeffectiveness and thereby a greater efficiency and lower emissions ofcontaminants and soot. Environmental pollution is lower, and thelifespan is prolonged.

Burners adjusted according to the air ratio do not react properly to allthe influences that change combustion, however, regardless of theirconstruction. Adjustment can thus sooner or later become inaccurate.This makes regular monitoring or calibration advantageous.

Typically, calibration is required because the air resistance in the airsupply duct or exhaust duct increases due to emission of soot or toforeign bodies. Rather less often, but equally affecting, is the reversecase, where the air resistance decreases because of unintentionalperforation of the ducts. Often, the inflow of air is determined by anexternal performance signal, and the control system adjusts the inflowof fuel to a reference control value corresponding thereto, even if theactual inflow of air no longer conforms to the performance signal.

Many a large burner senses the airflow volume, for example, via pressuresensors, and can thus compensate for changes to it to a certain extent.Sooner or later the sensor result will no longer be reliable, however.Simple burners rely exclusively on the air blower speed generated by aHall sensor or on the position of a flap resulting from electricalresistance measurement, or even just on the present actuating signal.

DE-A1-4429157 discloses a monitoring method for air ratio control.Changing of a second parameter as a result of the change in a firstparameter is observed, that is to say the changed value of the sensorsignal in response to a controlled, fixed change in an actuator. It isdecided, from the difference between this observation and storedreference values, whether a fault indication will be output.

DE-A1-4429157 did not specify for which types of sensor the monitoringmethod is suitable. The same applicant later described a completelydifferent calibration method specifically for burners in which thesensor for controlling the air ratio is formed by the ionisationelectrode. This is found in EP-A2-1002997, and will be describedhereinafter.

Control of the air ratio is particularly effective when the combustionquality can be directly or indirectly observed with a sensor. Typicallywith known burners, oxygen sensors are used in the exhaust gas duct,temperature sensors on the burner surface, or UV sensors in thecombustion chamber. These sensors are expensive, unreliable andhigh-maintenance for this purpose, and/or have a short lifespan.

Newer developments are based on the ionisation electrode that has beenused as standard for a long time for monitoring the flame in burners.Although it is not easy to evaluate its signal, the ionisation electrodedoes not have the disadvantages described hereinabove.

Any changes to the ionisation electrode typically require calibration.It can be changed by bending, wear or chemical attack to its surface, orby soiling with soot particles. The control system then attempts tostructure the combustion erroneously, such that measurements at areference control value based on an unchanged ionisation electrode arekept to.

According to EP-B1-770824, in order to calibrate a burner controlled byionisation flow where there is a fixed fuel flow volume, the air supplyis reduced from its controlled value, past a point where the ionisationsignal reaches its maximum stoichiometric value. This maximum isestablished. The difference between the newly established and thestored, previous maximum, allows the burner control to determine newreference ionisation values for the combustion at the desired air ratio.

By means of richer combustion, this method enables simple and reliabledetermination of a measured value without playing a role in at whatlevel of air supply this measured value is obtained or how theionisation signal depends exactly on the air supply.

Also in EP-A2-1002997 and DE-C1-19854824, calibration methods forionisation flow controlled burners have been described. These includesensing of a second measured signal that is representative of thepresent performance, even though in connection with the ionisationsignal. The second measured signal is always a second, different type ofionisation signal in DE-C1-19854824 and in particular instances inEP-A2-1002997.

In DE-C1-19854824, it is apparently assumed that the second ionisationsignal is barely sensitive enough for the instantaneous values of theburner performance in terms of measurement of the thermal electronoutput from the ionisation electrode. Similarly, according toEP-A2-1002997 a second ionisation signal can be generated that, incontrast to the first, is dependent upon the burner performance and theair ratio, and in fact with the aid of a special evaluation circuit isabsolutely no longer dependent upon the burner performance.

The known calibration methods do not at present change the normaloperation of the burner. Testing is simply done as to whether the burnerperformance and the air ratio from the different ionisation signals arestill in agreement with one another. When this is the case, the controlmethod remains unchanged. Only when certain threshold values have beenexceeded is it adapted.

Controlling adaptation takes place in DE-C1-19854824 in that the inflowdetermined from the performance signal, for example, the inflow of air,is changed until the second ionisation signal has an acceptable valueagain. Meanwhile, the other inflow is readjusted exactly as previously.In this way erroneous changes to the air ratio and to the burnerperformance should be reversed. As soon as a stable state is obtained,the first ionisation signal is measured. Lastly, this measured value isadopted as the new reference value for the first ionisation signal.

Provided that the second measured signal is reliable, this method cantest whether the correct air ratio is present, without affectingcontrolling. The changes required for any controlling adaptation areimmediately effective as they are simply to be directed towardsapproximation to the fixed value of the second measured signal or to thedesired relationship thereof to the ionisation signal.

SUMMARY OF THE INVENTION

The object of the invention is to make possible a control system thatimplements reliable and accurate calibration without large variations inthe air ratio.

According to a first aspect of the present invention, there is provideda control system for a burner with at least one ionisation electrodearranged in a flame region of the burner and with an actuating memberthat affects the amount of fuel or air supplied dependent upon anactuating signal, wherein the control system comprises an ionisationevaluation means connectable to the ionisation electrode, which meansgenerates an ionisation signal, a controller that generates a controlvalue x as value for the actuating signal at least periodicallydependent upon the ionisation signal, and a calibration unit to whichthe control value x is supplied and that, during calibration, afterchanging a reference control value, establishes one or more times avalue for the subsequent change in the control value x, and wherein acontrol system characteristic data for determining a value to beexpected there for are stored, wherein the calibration unit determinesthe differential value the established value and the expected value, andwherein the calibration unit in the control system newly determinesvalues by means of one or more such differential values.

Burners of the most varied design are possible as the burners, forexample, pre-mix gas burners or atmospheric burners with or withoutauxiliary blowers. In the case of atmospheric burners without auxiliaryburners, the airflow volume can be controlled, for example, by means ofan air flap or the like.

The first parameter that is changed during calibration is, for example,a reference value for control, that is to say a reference control value.Alternatively, a control parameter, the result of evaluation of anadditional measured signal, and so forth, can be selected.

For example, the first, as well as the second, parameter is part of thenormal control loop. The control loop can, however, also be interruptedat a point after the second and before the first parameter.

In an advantageous further development of the invention, while it ischanging, the second parameter is influenced by the ionisationelectrode.

The ionisation electrode has also proved to be a suitable sensor forthis purpose, and even for calibration for correcting the status,although it falls short of the desired air ratio range in terms ofaccuracy. Alternatively, an additional status sensor, such as a secondionisation electrode or an oxygen sensor, is used exclusively forcalibration.

In order to implement calibration according to the invention, thecalibration unit advantageously changes the first parameter on its owninitiative. Alternatively it waits until a suitable change is producedin the normal operation, for example by a stepwise increase of theexternal performance signal. The first parameter is then advantageouslykept constant while the second parameter is changing. Regardless of thedesign of the control system, however, alternative behaviour may bedemanded.

The calibration unit additionally determines a value to be expected forthe second parameter, and the difference thereof to the actual valuedetermined. With the aid of one or advantageously of several suchdifferential values, it then newly determines certain values.Differential values that were already determined during earliercalibration can also be used. Advantageously, the calibration unitweights the differential values such that the newer ones have a greaterweighting than the older ones.

If previous control has proved to be good enough for there to be norequirement for adaptation, certain calibration units according to theinvention newly determine the values such that they are allowed toremain the same.

If, however, the information acquired in calibration indicates thatprevious operation is unstable or unacceptable, certain calibrationunits according to the invention generate an alarm signal or shut downthe burner by changing appropriate values. In this broad sense,calibration can be considered not just as a correction, but additionallyor exclusively as monitoring for the burner operation.

If, however, an opportunity for adaptation is established, certaincalibration units according to the invention newly determine a storedreference control value, the value of which is adopted or triggered inthe specific control system in normal operation. This can occur in theform of a controlled correction or master control. Above all, it isintended that the air ratio be corrected to its earlier, desired value.Ideally, the performance delivered by the burner is also corrected back.Simpler variations of the invention do not do this in every case,however.

In control systems according to the invention, characteristic data fordetermining behaviour of the ionisation signal as a function of theperformance signal can be stored. Such a control system generates areference ionisation value appropriate for the behaviour, and itscontroller then controls the ionisation signal using the actuatingsignal. New determination of the ionisation reference value then takesplace, for example, in that a value dependent upon the performancesignal or a constant value is added or subtracted. The size of thisvalue is established by means of a function of the previously determineddifferential values, or else by master control that attempts toiteratively reduce the differential values sensed in the calibrations.

It has already been described hereinabove that the control systemaccording to the invention can determine the expected value of thechange in the second parameter, which is done using storedcharacteristic data. It has been shown that these characteristic dataare as a rule specific to the type of burner. They are determined orcalculated in a setting-up process with one or more burners, and copiesare stored in control systems for the same type of burner. This does notexclude another individual fine-tuning taking place when commissioningis done, for example to adjust construction tolerances.

In an advantageous further development of the invention, in order todetermine the expected value, the characteristic data include fordetermining behaviours of the second parameter to be expected withdifferent combustive contents of fuel and air.

The combustive content of the air is determined by means of its oxygencontent. This depends on the air pressure, the air temperature and thehumidity of the air. The combustive content of fuel relates to itsspecific energy content. During burner operation and from onecalibration to another the combustive content of both fuel and air canshow variations. When the control system takes into account thecombustive content during calibration, however, it can determine theexpected value of the change in the second parameter substantiallybetter.

In particular, the behaviours of the second parameter can be thosechanges expected after a specific change in the first parameter, thisbeing with different, but in each case steady, combustive contents offuel and air.

In an advantageous further development of the invention, before theirrespective changes, the calibration unit brings the first and the secondparameter to their respective initial values, which are thus differentfrom those in normal operation. In this way, changes in the parameterscan be adjusted, for the purpose of greater sensitivity, to an optimumoperating point. For example, the first parameter is returned in advanceto its initial value, and is monitored until the second has been broughtback to its corresponding initial value by means of the normal controlloop.

In an advantageous further development of the invention, the values tobe newly determined include an initial value for the first parameter,stored in the control system.

Master control can thus exist in that reference initial values improvedin the subsequent calibration are always present. Advantageously, thecalibration unit weights the initial values such that the newer ones aremore heavily weighted than the old ones. After a few times, thecalibration unit can then newly determine such values. For example, acorrection takes place in which, by adjusting the ionisation referencevalues under conditions of calibration, a fixed difference between theimproved initial value and the first control parameter can bere-established.

In an advantageous further development of the invention the values newlyto be determined include a reference control value that affects thedependency of the controller upon the performance signal.

A performance signal is understood as the signal that represents therequired performance. This further development enables correction of theperformance where there is a change in the supply of air or fuel that isnot compensated for by the control system.

According to a second aspect of the present invention, there is provideda method for setting-up a control system for a burner with at least oneionisation electrode arranged in a flame region of the burner, and withan actuating member that affects the amount of fuel or air supplieddependent upon an actuating signal, wherein the control system comprisesan ionisation evaluation means connected to the ionisation electrode,which means generates an ionisation signal, a controller that generatesthe actuating signal at least periodically dependent upon the ionisationsignal, and a calibration unit, and wherein the burner possiblycomprises additional sensors for establishing the quality of thecombustion, the burner is operated one or more times and thereby changesa first parameter, and a value for the subsequent change in a signalgenerated by a control loop is determined.

Normally, the setting-up process comprises measurements of a burner,wherein combustion is desirably in operation. The measurement resultscan be expanded by estimations that are based on expert knowledge or onthe type of burner.

The descriptions hereinabove with respect to the first parameter, thesecond parameter and the changes thereto are also valid in this case.

In setting-up control systems according to the invention, characteristicdata can be derived for determining the expected value for changing asecond parameter during calibration. The behaviour of the burner is thenobserved under varying conditions that are similar to the changes in theparameter during calibration, but do not necessarily correspond to them.

The characteristic data thus derived can be stored in further controlsystems according to the invention.

In an advantageous further development of the invention, the burner isalso operated at least once with a fuel with a different combustivecontent.

Advantageously, the specific energy content is reduced by at least 2%when the fuel is changed.

The setting-up process can also serve to refine any corrective measuresduring calibration. For this, measurements are carried out on modifiedburners that require correction of certain aspects. For example, theionisation electrode is replaced with an example with a very longoperating time, or an additional resistance is connected in series tothe ionisation electrode to simulate this. Further examples relate toits bending or covering with a coating or the installation of asignificant flow resistance in the air supply channel.

In an advantageous further development of the invention, the burner isset up at least once before operation in that the combustion no longerhas the desired air ratio prior to changing the first parameter and/orproduces the desired power output. At the end of such an operation thecombustion is improved in that a reference control value is newlydetermined.

From the newly determined reference control value, characteristic datacan be derived for newly determining values during calibration.

In an advantageous further development of the invention, the burner isset up prior to operation such that an additional resistance isconnected in series to the ionisation electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an ionisation evaluating means in acontrol system according to the invention,

FIG. 2 shows a block diagram of the control system, and

FIG. 3 shows the expected behaviour of the actuating signal of thecontrol system in the case of four different combustion contents andwith different air ratios.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows schematically the principle of functioning of an ionisationevaluating means 14 in a control system in accordance with theinvention. In an equivalent circuit, the flame 1 is represented by adiode 1 a, and a resistance 1 b. An alternating voltage of, for example,230V, is applied via L and N. When a flame 1 is present, because of theflame diode 1 a a greater current flows through the blocking capacitor 3in the positive half-wave than in the negative half-wave. In this way, apositive direct voltage U_(B) forms between L and a resistance 2 fittedfor the purpose of shock protection, at the blocking capacitor 3.

A direct current thus flows through a decoupling resistor 4 from N tothe blocking capacitor 3. The level of direct current is dependent uponU_(B) and thus directly upon the flame resistance 1 b. The flameresistance 1 b also affects the alternating current through thedecoupling resistor 4, although to a different extent compared to thedirect current. Consequently, a direct current and an alternatingcurrent flow through the resistance 4, as described above.

A high pass filter 5 and a low pass filter 6 are connected after theresistance 4. The alternating current is filtered out by means of thehigh pass filter 5, and the direct voltage component is blocked off. Thedirect voltage component dependent upon the flame resistance 1 b isfiltered out by means of the low pass filter 6, and the alternatingcurrent is substantially blocked off. The alternating current flowingfrom the high pass filter 5 is amplified in an amplifier 7, and areference voltage U_(Ref) is added to it. In an amplifier 8 the directcurrent flowing from the high pass filter 6 is amplified with possiblesmall alternating current components, and the reference voltage U_(Ref)is added to it.

The reference voltage U_(Ref) can be selected as desired, for exampleU_(Ref)=0, but is preferably selected such that the amplifiers andcomparators require only one supply.

At a comparator 9, the alternating voltage output by the amplifier 7 andthe direct voltage output by the amplifier 8 are compared to oneanother, and a pulse width modulated (PWM) signal is generated. If theamplitude of the system voltage changes, the alternating voltage anddirect voltage change in the same proportion, but the PWM signal doesnot change. The signal deviation of the PWM signal can be adjusted bymeans of the amplifiers 7 and 8 in a broad range between τ=0 and τ=50%pulse duty factor.

The direct voltage component U= is compared in a comparator 10 to thereference voltage U_(Ref). If a flame is present, the direct voltagecomponent is greater than the reference voltage (U=>U_(Ref)) and thecomparator output of the comparator 10 switches to 0. If no flame ispresent, the direct voltage component is approximately equal to thereference voltage (U=≈U_(Ref)). Because of this, the small alternatingvoltage component superimposed on the direct voltage component that isnot filtered out by the low pass 6, the direct voltage component brieflyfalls below the reference voltage and pulses appear at the comparatoroutput of the comparator 10. These pulses are supplied to a monoflop 11that is not triggered.

The monoflop 11 is triggered such that the pulse sequence output by thecomparator 10 comes faster than the pulse duration of the monoflop.Thus, when no flame is present, a 1 appears constantly at the output ofthe monoflop. If a flame is present, the monoflop is not triggered and a0 appears permanently at the output The monoflop 11 not triggeredconsequently forms a “missing pulse detector” that converts the dynamicon/off signal into a static on/off signal.

Both signals, the PWM signal and the flame signal, can now be furtherprocessed separately or be interlaced by means of an OR element 12. Asan output of the OR element 12, where flames are present a PWM signalappears, the pulse duty factor of which is a value for the flameresistance 1 b. This ionisation signal 13 is supplied to a controller 26shown in FIG. 2. Where no flame is present, the output of the OR elementis permanently set at 1. The ionisation signal 13 can be transmitted viaan optical coupler, not shown, in order to obtain protective separationbetween the supply side and the safety extra-low voltage side.

FIG. 2 shows schematically a block diagram of a control system 15according to the invention.

An ionisation electrode 16 projects into the flames 1. A gas valve 17 iscontrolled by an actuating signal 18 in a direct or indirect manner, forexample by means of a motor. Alternatively another mechanical pressurecontroller is inserted.

An air blower 19 is controlled to a speed that is used here as an inputparameter. It is assumed that the speed corresponds to a performance 22requirement. A speed signal 20 is supplied via a filter 21 to a controlunit 23 that is designed as part of a program for running in amicroprocessor. Here, characteristic data are stored that establish thecharacteristic curves of a first and a second control signal 24 and 25.A controller 26 weights and adds together the two control signals andthus determines the actuating signal 18. This processing of the controlsignals is dependent upon the ionisation signal 13.

The ionisation signal 13 is firstly smoothed by the controller 26,firstly by means of a low pass filter 27, in order to suppress glitchesand instabilities. In a comparator 28, a reference signal generated bythe control unit 23 and supplied via a corrective unit 29 is subtracted.From the sequence signal of this processing of the ionisation signal, aninternal control value x is determined from a proportional controller 31and a parallel integrating unit 32, which value weights the two controlsignals 24 and 25, and thereby finely adjusts the actuating signal 18.

The control value x can alternatively be generated by a PID controlleror a status controller from the sequence signal.

The control value x is additionally supplied to a calibration unit 36 asa value for the actuating signal 18.

The calibration unit 36 includes a clock that triggers calibrations atregular intervals. When it is time, the calibration unit 36 firstlybrings the air blower speed to a fixed, predetermined value, and in afixed, predetermined step increases the reference signal 30 in order toeasily bring the system closer to the stoichastic combustion point in asensitive working region.

After this it senses the steady state control value x as an index forthe current combustive content of fuel and air.

The calibration unit 36 then increases the reference signal 30 again ina second, predetermined step. This forms the change in the firstparameter that is important with respect to the invention, namely thereference signal 30. In response to this, the controller 26 governs theactuating signal 18 by reducing the control value x to a yet ratherricher combustion.

After 12 seconds, when the control value x is in its steady state again,it is sensed again. The comparison with its initial value forms thechange in a second parameter, namely the control value x.

Using stored characteristic data, the calibration unit 36 calculates anexpected value 40 for the changed control value x with the prevailingcombustive content, and subtracts from it the actual changed controlvalue x. A possible difference is an index that the air ratio in normaloperation does not have the value desired, and combustion was too richor too lean.

The expected value 40 for the changed control value x is produced byadding its initial value and its expected change together. The expectedchange in the control parameter x again results from a third orderpolynominal development of its initial value, the constants of whichwere determined in a setting up process and were stored ascharacteristic data in the control system.

By means of an exponential weighting, the calibration unit 36 nowaverages the differential value with the average value of thedifferential values of previous calibration, such that the newer onesare more heavily weighted than the older ones.

If the average value thus newly determined exceeds certain thresholds,the calibration unit 36 indicates emergency operation or even shuts downoperation.

When this is not the case, when a low threshold value is gone below, thecalibration unit 36 passes generation of the reference signal 30 to theactuating unit 23, in that with each speed signal 20 it adds orsubtracts a small value. Accordingly, combustion in normal operation ismade a little richer or leaner.

Instead of this, an alternative calibration unit according to theinvention modifies the two steps to the same extent, in that thereference signal 30 is increased at the beginning of the nextcalibration. Only with every tenth calibration does it pass generationof the reference signal 30, because its consequently improved values, tothe actuating unit 23.

By repetition, the air ratio in normal operation is moved iterativelytowards its desired value.

FIG. 3 shows schematically the behaviour of the actuating signal 18 as afunction of the speed signal 20 in a properly set-up burner. It alsoshows how the actuating signal would change, according to expectations,if an increase 39 in the reference signal 30 takes place in normaloperation, and thereby a richer combustion.

The surfaces shown represent certain, different combustive contents offuel and air. The front edges of the upper and lower surface form thecharacteristic curves of the control signals 24 and 25. They each relateto a fuel with a rather high and respectively a rather low calorificvalue, and are established in a setting-up process from each of fourmeasurement points, not shown, as a polynominal development.

In normal operation, as a rule the fuel has an average combustivecontent. This is shown by the surface with the broken line edge. Thecontrol system 15 controls the actuating signal 18 by means of weightingof the control signals 24 and 25 to an almost optimum value 33 for thedesired air ratio. This fine controlling corresponds to matching, interalia, of the prevailing combustive content of fuel and air andcorresponds to a vertical movement in FIG. 3.

If there is now a stepwise increase in the performance requirement 22and a corresponding change in the speed signal 20 takes place, theweighting of the two control signals 24, 25 remains largely unaffected.The control signals 24 and 25 themselves increase quickly with thechange in speed to their respective higher values along thecharacteristic curves, and the actuating signal 18 also increasesrapidly to the value 34. This controlled value 34 of the actuatingsignal 18 is normally already very accurate, that is to say close to anoptimum value for the desired air ratio.

As soon as the ionisation signal 13 has balanced itself to the newstatus, typically after a few seconds, the weighting of the controlsignals 24 and 25 are further refined, and in FIG. 3 the actuatingsignal 18 normally moves only a little, vertically.

However, should the actuating signal 18 nevertheless correct itself to avarying value 35, a fault signal or correction of the reference signal30 is required. An alternative calibration unit according to theinvention uses this accuracy in the control signals 24 and 25 forestablishing the actuating signal 18 shortly after a change in thespeed, and then again after the system has reached a steady state.

At the beginning, however, the calibration unit 36 firstly adjusts theair blower speed and the reference signal 30 to values that, in the caseof a properly set-up burner, correspond to a point 37 in FIG. 3. Inpractice, it can be assumed that the system has consequently beenbrought into a more sensitive working area.

After acquiring the steady state control value x as the index for thecurrent combustive content of fuel and air, in a second step thecalibration unit 36 increases the reference signal 30 again, which inthe case of a properly set-up burner corresponds to moving to a point38.

The expected value 40 for the latterly described change in the controlvalue x thus corresponds to the height difference between points 37 and38 in FIG. 3. It is added to the initial value of the control value x.After 12 seconds a comparison with the actual, changed control value xtakes place. This leads to possible corrective measures or faultsignals.

The characteristic data required for calculating the expected value 40are previously derived in a setting up process using control valuemeasurements with in total three different known combustive contents offuel and air.

Additionally, the reference signal 30 is increased with the same stepsfrom its value during normal operation, firstly to reach the moresensitive working area and then in order to determine the subsequentchange in the control value x. In FIG. 3 the actuating signal valuescorresponding to the measurements of the control value x are representedby small circles.

In fact, the constants of an accurate third order polynominaldevelopment for the steady state control value x are thus found for theexpected value for its change. The steady state control value xrepresents the prevailing combustive content of fuel and air. It hasbeen shown that it represents the combustive content sufficientlyaccurately, even if the air ratio varies in normal operation from theair ratio desired, or if the combustive content of fuel and air changesagain within the usual bounds during calibration.

While it is superfluous for simple calibrations, the setting-up processcan alternatively be refined in that characteristic data areadditionally determined at different speed values. Calibration is alsoperformed at these speeds.

An alternative calibration unit according to the invention can, interalia, determine a possible fault in this way, namely in particularwhether the flow resistance of air or fuel has changed. In such a case,the alternative calibration unit newly calibrates the speed signal 20 inorder to correct the power output back. This relates not just to thecharacteristic curve for generating the reference value signal 30 butalso, for example, to the two characteristic curves of the controlsignals 24 and 25.

1. Control apparatus for a burner, having at least one ionizationelectrode disposed in a flame region of the burner, and having anactuating element, which influences the feed quantity of fuel or air independence upon an actuating signal, the control apparatus at leastbeing equipped with an ionization analyzer, which is connecteddownstream of the ionization electrode and generates an ionizationsignal, and having a controller, which generates a control value x asmeasure of the actuating signal, at least occasionally in dependenceupon the ionization signal, the control value x being fed to acalibrating unit, wherein the calibrating unit establishes one or moretimes after the change in a control set value the consequential changein the control value x, and in that the calibrating unit determines, onthe basis of characteristic data stored in the control apparatus, anexpected value for the changed control value x, and in that thecalibrating unit performs at least one comparison between theestablished change in the control value x and the expected value, and inthat, independently from the comparison result, and the calibrating unitnewly determines, using one or more differential values acquired fromthe comparison, the control set value stored in the control apparatus,or generates a disturbance signal.
 2. Control system for a burneraccording to claim 1, wherein, during its changing, the control value xis affected by the ionisation electrode.
 3. Control system for a burneraccording to claim 1, wherein the characteristic data for determiningthe expected value include characteristic data for determining thebehaviour of the control value x to be expected with differentcombustive contents of fuel and air.
 4. Control system for a burneraccording to claim 1, wherein, prior to their respective changes, thecalibration unit returns the control set value and the control value xto their initial values.
 5. Control system for a burner according toclaim 4, wherein the values to be newly determined include an initialvalue for the control set value stored in the control system.
 6. Controlsystem for a burner according to claim 1, wherein the control set valueto be newly determined affects the dependency of the controller upon theionisation signal.
 7. Method for adjusting a control system for a burnerhaving at least one ionization electrode disposed in a flame region ofthe burner, and having an actuating element, which influences the feedquantity of fuel or air in dependence upon an actuating signal, thecontrol system at least being equipped with an ionization analyzer,which is connected downstream of the ionization electrode and generatesan ionization signal, and having a controller, which generates a controlvalue x as measure of the actuating signal, at least occasionally independence upon the ionization signal, the control value x being fed toa calibrating unit, wherein, during a calibration, the burner isoperated one or more times and a control set value is hereupon changedand the consequential change in the control value x determined, andduring the calibration, characteristic data for determining anexpectancy value for the changed control value x are derived and arestored in the control apparatus.
 8. Method for adjusting a controlsystem according to claim 7, wherein the burner is also operated atleast once with a fuel with a different combustive content.
 9. Methodfor adjusting a control system according to claim 7, wherein the burneris adjusted at least once prior to operation such that prior to changingthe control set value, the combustion no longer has the desired air/fuelratio and/or no longer generates the desired performance, and at the endof such operating, the combustion is improved in that a control setvalue is newly determined.
 10. Method for adjusting a control systemaccording to claim 9, wherein, prior to operation, the burner isadjusted in that an additional resistance is connected in series to theionisation electrode.
 11. A control system for a burner comprising: acontroller that, based upon a signal from an ionization sensor, isconfigured to generate an actuating signal for an actuating member thataffects the amount of fuel or air supplied to the burner, the actuatingsignal based on a control signal x, the control signal x being generatedby the controller based on the signal from the ionization sensor; and acalibration unit configured to generate an output signal based upon adifference between an estimated expected value and an actual value ofthe control signal x, wherein the controller is configured to generatethe actual value after changing a parameter from a first value to asecond value and the estimated expected value is calculated usingpredetermined characteristic data.
 12. The system of claim 11, whereinthe calibration unit is configured to generate the output signal basedupon a weighted average of a plurality of differences between estimatedexpected values and actual values of the control value x, wherein thecontroller is configured to generate the actual values such that theactual values result from changing the parameter from first values tosecond values and the estimated expected values are calculated using thepredetermined characteristic data.
 13. The system of claim 12, whereinthe calibration unit is configured such that the plurality ofdifferences are weighted that a recently determined difference isweighted more heavily than a less recently determined difference. 14.The system of claim 11, wherein the calibration unit is configured touse the output signal for at least one of a reference control signal, analarm signal or a shutdown signal.